Monday 26th
10:00 Registration
11:00 Welcome
Session I (Chair: Prado Martín-Moruno)
11:15 Lucas Lombriser (University of Geneva): Cosmic Self-Acceleration from Modified Gravity before/after GW170817
12:00 Frederico Arroja (IA-Lisbon): Large-scale structure in mimetic Horndeski gravity
12:15 Héctor Villarubia-Rojo (Universidad Complutense de Madrid): Constraints on hidden gravitons from fifth-force experiments and stellar energy loss
12:30 Lunch
Session II (Chair: Lucas Lombriser)
14:00 Ana Paulino-Afonso (IA-Porto): The end of the reionisation: what are the most luminous Lyman-a emitters telling us?
14:15 Pablo Diez-Valle (Universidad Complutense de Madrid): Grand Unified Theories in Cosmology
14:30 Rita Neves (IA-Lisbon): Dynamics in Loop Quantum Cosmology
14:45 José Ricardo Correia (IA-Porto): GPGPU Anisotropic Domain Walls
15:00 Franco Dante Albareti (Instituto de Física Teórica (IFT, UAM+CSIC)): Massive scalar fields on hot FRW geometries
15:15 Ivan Rybak (IA-Porto): Analytic approach to the cosmic (super)string network evolution with junctions
15:30 Coffee break
Session III (Chair: Mariam Bouhmadi-López)
16:00 Asier Lopez-Eiguren (University of Helsinki): Evolution of semilocal strings: lengths and velocities
16:15 Andrew Liddle (IA-Lisbon): Testing gravity on cosmological scales
16:30 Noemi Frusciante (IA-Lisbon): Cosmological tests of gravity beyond general relativity
16:45 Tomás Silva (Centro de Astrofísica da Universidade do Porto): Current and future constraints on extended Bekenstein-type models for a varying fine-structure constant
17:00 Ana Marta Pinho (ITP Heidelberg): Model-independent measurement of the anisotropic stress parameter η
17:15 Carlos Martins (IA-Porto), Constraining late-time dark energy phase transitions
17:30 Ana Alonso-Serrano (Max Plank Insitute for Gravitational Physics): GUP impact onto the black holes information flux
18:30 Public talk. Carlos Martins (IA-Porto): O Projecto ELT: Como se Prepara uma Revoluçao (in Portuguese)
Tuesday 27th
Session IV (Chair: Miguel Zumalacárregui)
09:00 Van de Bruck (University of Sheffield): Equivalence principle violations in the dark sector
09:45 Sante Carloni (CENTRA – Instituto superior Tecnico), Generalising the coupling between spacetime and matter
10:00 Elsa Teixeira (IA-Lisbon): Conformally coupled tachyonic dark energy
10:15 Diogo Castelão (IA-Lisbon): Testing structure formation in Unified Dark matter-energy models
10:30 Coffee break
Session V (Chair: Gonzalo J. Olmo)
11:00 Luis Ventura (CIDMA & Departamento de Física ,Universidade de Aveiro): Warm Little inflaton dark matter
11:15 Carlos Garcia-Garcia (IFF-CSIC): Dark energy from alpha-attractors: phenomenology and observational constraints
11:30 Francisco Pedro (Università di Bologna): Primordial black holes from single field inflation
11:45 Miguel Zumalacárregui (UC Berkeley & IPhT Saclay): No LIGO MACHO
12:00 José M. Sánchez Velázquez (Universidad Complutense de Madrid): Dark Matter gravitational production in Reheating
12:15 Catarina Cosme (University of Porto): Scalar field dark matter with spontaneous symmetry breaking and the 3.5 keV line
12:30 Lunch
Session VI (Chair: Sante Carloni)
14:00 Clara Alvarez-Luna (Universidad Complutense de Madrid): Topological Dark Matter and PeV neutrinos
14:15 Javier Rubio (Heidelberg University): Primordial black holes from fifth forces
14:30 Tiago Barreiro (Universidade Lusófona): Removing the σ8 tension with coupled quintessence
14:45 Angeles Moliné (IA-Lisbon): Characterization of dark matter subhalo structural properties
15:00 Gonzalo J. Olmo (University of Valencia & CSIC): Modified gravity without modified gravity
15:15 Victor I. Afonso (U. Federal de Campina Grande (UFCG)): Scalar Geons in Born-Infeld Gravity
15:30 Joao Luis Rosa (CENTRA – Instituto Superior Técnico): Cosmological solutions in generalized hybrid metric-Palatini gravity
15:45 Announcement of Ibericos 2019
17:00 – 19:00 Tour of Lisbon
20:00 Conference dinner at “THE GRÉMIO LITERÁRIO”
Wednesday 28th
Session VII (Chair: Joao Rosa)
09:00 David Mulryne (Queen Mary University of London): Numerical tools for multifield inflation
09:45 Pedro Carrilho (Queen Mary University of London): General initial conditions for second order Boltzmann solvers
10:00 Jesús Torrado Cacho (University of Sussex): Parameter estimation in Cosmology: new methods and new tools
10:15 Mar Bastero-Gil (University of Granada): Adiabatic out-of-equilibrium solutions to the Boltzmann equation
10:30 Coffee break
Session VIII (Chair: Mar Bastero-Gil)
11:00 Prado Martín-Moruno (Universidad Complutense de Madrid): Avoiding the Big Rip in f(R) quantum cosmology
11:15 Mariam Bouhmadi-López (University of Basque Country): Classical and quantum approach to the little sibling of the big rip
11:30 Miguel Aparicio Resco (Universidad Complutense de Madrid): Model independent parametrization of growth in modified gravity
11:45 Gabriel Farrugia (University of Malta): Cosmological reconstructed solutions in extended teleparallel gravity theories with a teleparallel Gauss-Bonnet term
12:00 Lara Sousa (IA-Porto): On the matter Lagrangian of particles and fluids
12:15 Rui Azevedo (IA-Porto): Perfect fluid Lagrangian and its cosmological implications in non- minimally coupled theories of gravity
12:30 Lunch
Session IX (Chair: Victor Afonso)
14:00 Marina Cortes (IA-Lisbon): Irreversibility in Foundational Cosmology
14:15 Claudio Gomes (Departamento de Física e Astronomia, FCUP e CFP): Gravitational waves in theories with a non-minimal curvature-matter coupling
14:30 Ricardo Zambujal Ferreira (U. Barcelona): Thai-flation
14:45 Francisco Cabral (IA-Lisbon): Phase transition with U(1) symmetry breaking in Einstein- Cartan-Theory
15:00 Bruno Barros (IA-Lisbon): Traversable wormholes with 3-forms
15:15 Joao Rosa (University of Aveiro): Black hole Lasers powered by Axion Superradiant instabilities
15:30 Announcement of the winner of Best Presentation Award sponsored by the Journal Universe.
LIST OF ABSTRACTS (in order of appearance)
Lucas Lombriser: Cosmic Self-Acceleration from Modified Gravity before/after GW170817
Modifications of gravity have long been considered as an alternative explanation for the late-time accelerated expansion of our Universe. The recent gravitational wave measurement GW170817 with its electromagnetic counterparts brought the challenge to the concept of cosmic self-acceleration from modifying gravity that had been anticipated for such an event. I will first discuss why a rigorous discrimination between acceleration from modified gravity and from a cosmological constant or dark energy was not possible with observations of the large-scale structure alone and how that measurement has particularly impacted the landscape of scalar-tensor gravity theories. I will conclude with an outlook on how surviving self-accelerated models will ultimately only be exhaustively probed with a large number of Standard Sirens. Finally, I will sketch new concepts that have been brought forward of how an evolving speed of gravity may nevertheless be the driver of cosmic acceleration yet remain compatible with the tight GW170817 constraint.
Frederico Arroja: Large-scale structure in mimetic Horndeski gravity
In this talk, I shall propose to use the mimetic Horndeski model as a model for the dark universe. Both cold dark matter (CDM) and dark energy (DE) phenomena are described by a single component, the mimetic field. In linear theory, I will show that this component effectively behaves like a perfect fluid with zero sound speed and clusters on all scales. For the simpler mimetic cubic Horndeski model, if the background expansion history is chosen to be identical to a perfect fluid DE (PFDE) then the mimetic model predicts the same power spectrum of the Newtonian potential as the PFDE model with zero sound speed. In particular, if the background is chosen to be the same as that of LCDM, then also in this case the power spectrum of the Newtonian potential in the mimetic model becomes indistinguishable from the power spectrum in LCDM on linear scales. A different conclusion may be found in the case of non-adiabatic perturbations. I will also discuss the distinguishability, using power spectrum measurements from LCDM N-body simulations as a proxy for future observations, between these mimetic models and other popular models of DE. For instance, one finds that if the background has an equation of state equal to -0.95 then one will be able to distinguish the mimetic model from the PFDE model with unity sound speed. On the other hand, it will be hard to do this distinction with respect to the LCDM model. Talk based on: https://arxiv.org/abs/1708.01850
Héctor Villarrubia-Rojo: Constraints on hidden gravitons from fifth-force experiments and stellar energy loss
We study different phenomenological signatures associated with new spin-2 particles. These new degrees of freedom, that we call hidden gravitons, arise in different high-energy theories such as extra-dimensional models or extensions of General Relativity. At low energies, hidden gravitons can be generally described by the Fierz-Pauli Lagrangian. Their phenomenology is parameterized by two dimensionful constants: their mass and their coupling strength. In this work, we analyze two different sets of constraints. On the one hand, we study potential deviations from the inverse-square law on solar-system and laboratory scales. To extend the constraints to scales where the laboratory probes are not competitive, we also study consequences on astrophysical objects. We analyze in detail the processes that may take place in stellar interiors and lead to emission of hidden gravitons, acting like an additional source of energy loss. Reference: JHEP 1709 (2017) 104, arXiv:1706.07818
Ana Paulino-Afonso: The end of the reionisation: what are the most luminous Lyman-a emitters telling us?
The reionisation was a crucial milestone in the history of the Universe that provides us an opportunity to study the properties of the first galaxies and stars as well as to understand the physics of large scale structure formation. One key observable that could be very efficient in tracing the neutral hydrogen content and its spatial distribution is the Lyman-a emission from galaxies. This is an independent measure of the reionisation from the Gunn-Peterson trough observations in quasar spectra. I would like to review the last results based on Lyman-a emitting galaxies that trace the history of the Universe in the first billion years. I will focus my contribution on the nature of the most luminous of these sources, in particularly, in their sizes and the detection of their diffuse halos. Are the most luminous Lyman-a emitters found so far an essential piece to better understand when and how reionisation occurred and be reconciled with results from CMB experiments like Planck?.
Pablo Díez-Valle: Grand Unified Theories in Cosmology
The Standard Model of particles physics (SM), which describes the strong, weak and electromagnetic interactions, has shown to be very successful. However, there are clear indications that the SM is not the ultimate theory of elementary particle interactions since it has troubles to explain some phenomena such as the neutrino masses. It is known that some of these problems could be resolved considering a gauge theory with invariance under a larger group than the SM gauge group. Thereby the Standard Model would be the low-energy limit of this new gauge theory. We call them Grand Unified Theories (GUTs). Most of GUTs have important implications in Cosmology, for example an explication for the baryon asymmetry of the universe, new dark matter candidates, an approach to the earliest universe energies… We will introduce Grand Unification and we will discuss its role in Cosmology. Furthermore, we shall present an unification model based in gauge group $SU(4)_C \times SU(4)_L \times SU(4)_R$, and we will show how this model can introduce new dark matter candidates.
Rita Neves: Dynamics in Loop Quantum Cosmology
The dynamics of a flat FLRW cosmological model with a massless scalar field has been intensively studied in the context of Loop Quantum Cosmology (LQC), leading to the resolution of the big-bang singularity in terms of a quantum bounce. In this talk, after reviewing the main aspects and results of this analysis, I will present a method to approximately solve the quantum dynamics when the potential of the scalar field does not vanish. I will apply this method to the simple case of a constant potential.
José Ricardo Correia: GPGPU Anisotropic Domain Walls
Cosmic strings and other topological defects arise naturally in many proposed theories of new physics beyond the standard model unifying the electroweak and strong interactions, as well as in many Type-IIB brane inflation models, where horizon sized superstrings are produced as a result. In both cases the need for higher resolution and extra complexity to model realistic defects, can heavily tax the underlying hardware (to the point where unfeasible amounts of time and resources are necessary). This is also evident in recent observational progress which highlights that cosmic string network simulations are already bottlenecked. One can expect this problem to be aggravated, if one considers next-generation facilities such as CORE and LISA.
A solution is to try to optimise and/or parallelise existing code, providing faster and more scalable simulations. We hereby present an effort in this direction, a prototypical General Purpose Graphics Processing Unit (GPGPU) computing implementation of a network of the simplest defects “domain walls”. We show the significant speed-ups that incur from parallelising the code, and study possible errors by comparing sequential and parallel simulations and any possible effects on scaling from using single or double precision. As a further form of validation, we attempt to show how successful the recently extended Velocity-dependent One-Scale (VOS) model for domain walls is at describing domain walls produced at an anisotropic era, frozen in comoving coordinates in some open inflationary epoch, by continuing previous studies.
Franco Dante Albareti: Massive scalar fields on hot FRW geometries
We study possible effects of classical gravitational backgrounds on the dynamics of a massive scalar field computing one-loop corrections induced by its self-interactions. Vaccum and finite temperature contributions to the energy-momentum tensor and the effective potential are described. Our approach is based on the explicit mode decomposition of the field in the preturbed geometry instead of the local approach based on the Schwinger-De Witt expansion. For vaccum contritributions, we discuss two different regularization procedures: a cutoff and dimensional regularization. On the other hand, thermal corrections show that global thermal effects in a curved spacetime can be encoded in the local Tolman temperature at leading order in perturbations and in the adiabatic expansion.
Ivan Rybak: Analytic approach to the cosmic (super)string network evolution with junctions.
The brane type of inflation might have left a particular observational remnant – cosmic superstring. By studying the observational signal from the network of these strings, one can obtain an additional constraint on brane inflation. Unlike the usual cosmic strings, superstrings posses peculiar properties, which influence their evolution. In particular, cosmic supersting posses different tensions, which leads to junctions production due to strings collisions. Possible decrease/increase of strings length caused by these junctions, gives rise to the energy exchange between strings. This feature is important for the network evolution and should be quantified. One way to do it is to use the semi-analytic velocity-depend one scale (VOS) model.
In this work we generalize the description of cosmic strings collisions, in particular for expanding universe. We present details of junctions dynamics after string collisions and probability for the grow/decrease of their lengths. By implementing these results to the averaged cosmic string network, we obtain the VOS model with dynamical junctions.
Asier Lopez-Eiuguren: Evolution of semilocal strings: lengths and velocities
In this talk I will present an important step for the comprehensive numerical study of semilocal string networks and their cosmological evolution. These can be thought of as hybrid networks comprised of (non-topological) string segments, whose core structure is similar to that of Abelian Higgs vortices, and whose ends have long–range interactions and behaviour similar to that of global monopoles. I will introduce a new algorithm to identify the position of the segment cores. This allows to determine the length and velocity of each individual segment and follow their evolution in time. Using the new method, statistical distribution of segment lengths and velocities for radiation- and matter-dominated evolution in the regime where the strings are stable will be shown. The new segment detection algorithm gives higher length values than
previous studies based on indirect detection methods. The statistical distribution shows no evidence of (anti)correlation between the speed and the length of the segments.
Andre Liddle: Testing gravity on cosmological scales
We use a range of cosmological data to constrain phenomenological modifications to general relativity on cosmological scales, through modifications to the Poisson and lensing equations. We include cosmic microwave background anisotropies measurements from the Planck satellite, cosmic shear from CFHTLenS and DES-SV, and redshift-space distortions from BOSS data release 12 and the 6dF galaxy survey. We find no evidence of departures from general relativity.
Noemi Frusciante: Cosmological tests of gravity beyond general relativity
Given the wide sample of dark energy and modified gravity models (DE/MG) that address late time accelerated scenario and the high precision data, it becomes crucial to test DE/MG theories against data on large scales. In the quest of a model independent parametrization for gravity theories, the effective field theory formalism (EFT) has been applied to the phenomenon of cosmic acceleration. It is developed by using a perturbative approach in which an extra scalar degree of freedom appears only at the level of perturbations. I will present the implementation of this framework into CAMB/CosmoMC creating, what we dubbed, EFTCAMB/EFTCosmoMC. These patches allow to test gravity theories with the most recent data releases. To illustrate the use of these patches, I will show some results about some well known cosmological models and also some agnostic parametrizations of the underlying theory of gravity in light of Gws constraints. Moreover, irrespectively of the MG model adopted, one has to ensure that the evolution of the modes associated to the extra DoF does not lead to pathological instabilities, such as ghost, gradient and tachyonic instabilities. I will present the importance of having the correct viable space when testing gravity models.
Tomás Silva: Current and future constraints on extended Bekenstein-type models for a varying fine-structure constant.
There is a growing interest in astrophysical tests of the stability of dimensionless fundamental couplings, such as the fine-structure constant α, as an optimal probe of new physics. The imminent arrival of the ESPRESSO spectrograph will soon enable significant gains in the precision and accuracy of these tests and widen the range of theoretical models that can be tightly constrained. Here we illustrate this by studying proposed extensions of the Bekenstein-type models for the evolution of α that allow different couplings of the scalar field to both dark matter and dark energy. We use a combination of current astrophysical and local laboratory data (from tests with atomic clocks) to show that these couplings are constrained to parts per million level, with the constraints being dominated by the atomic clocks. We also quantify the expected improvements from ESPRESSO and other future spectrographs, and briefly discuss possible observational strategies, showing that these facilities can improve current constraints by more than an order of magnitude.
Ana Marta Pinho: Model-independent measurement of the anisotropic stress parameter η
The observation of the neutron star merger GW170817 along with its electromagnetic counterpart has set a strong constraint on the value of the speed of gravitational waves to be very close to the one of the speed of light. This result also gives information on the validity of some modified gravity theories as well on its parameters. In this work, we constrain the anisotropic stress parameter η in a model-independent way, without assumptions on the initial conditions or Dark Matter. The correspondence between this model-independent relation and the quasistatic limit for a Horndeski Lagrangian makes these constraints a test for this class of Dark Energy models. The recent available data of Hubble expansion rate, Redshift Space Distortions and Lensing observables enables this analysis and we account for the problem of data reconstruction by comparing three different methods. Our results are compatible with the standard LCDM scenario, that is η=1, however it departs from that value at z > 0.7.
Carlos Martins: Constraining late-time dark energy phase transitions
I will discuss (on the blackboard) a broad class of varying alpha models which can all be seen as extensions to the simple canonical BSBM model. Treating them with a common formalism enables a first quantitative comparison of the whole class of models to current local, astrophysical and cosmological data, and I will present the results of this analysis. Time permitting I will also discuss the improved constraints expected from ESPRESSO and ELT-HIRES.
Ana Alonso-Serrano: GUP impact onto the black holes information flux
We have investigated the generalized uncertainty principle (GUP) modification of the entropy budget of a black hole evaporation process, as well as the corrections to the sparsity of the Hawking radiation at the late stages of evaporation. We have found that due to these quantum gravity motivated corrections, the entropy flow per particle reduces its value on the approach to the Planck scale. We have also showed that the radiation flow is no longer sparse when the mass of a black hole approaches Planck mass.
Carsten van de Bruck: Equivalence principle violations in the dark sector
In this talk I will review models in which dark matter particles couple directly to a dark energy scalar field. Such theories predict a fifth force in the dark sector. After a review of the cosmological consequences of such models I will present the latest constraints on such interactions. I will also discuss other tests of such theories, which go beyond the CMB or large scale structures.
Sante Carloni: Generalising the coupling between spacetime and matter
I explore the idea that the coupling between matter and spacetime is more complex than the one originally envisioned by Einstein. I propose that such coupling takes the form of a new fundamental tensor in the Einstein field equations. The introduction of this tensor can account for dark phenomenology in General Relativity, maintaining a weak field limit compatible with standard Newtonian gravitation. The same paradigm can be applied any other theory of gravitation.
Elsa Teixeira: Conformally coupled tachyonic dark energy
Models which rely on scalar fields to explain the late time acceleration of the Universe have been the focus of many studies in the context of Dynamical Systems. In this talk I will present a dark energy model in which a tachyonic field with an inverse square potential is conformally coupled to a barotropic perfect fluid. A detailed analysis of the cosmological effects is performed in comparison with the previously studied uncoupled tachyonic dark energy for which there exists only one stable critical point that gives late time acceleration of the Universe. I also compare this set up with previously studied coupled models.
Diogo Castelao: Testing structure formation in Unified Dark matter-energy models
UDM models usually have oscillations in the matter power spectrum caused by a non-zero speed of sound, which cause difficulties in an MCMC sampling of the parameter space. In this talk, I will test an UDM model with fast transition using weak lensing and CMB data, using both MCMC and Nested sampling algorithms. The second method is found to be considerably better. I will also enumerate some issues relevant for future Euclid tests of UDM models.
Luis Ventura: Warm Little inflaton dark matter
We discuss the possibility of the inflaton naturally accounting for all the dark matter in the Universe within the warm inflation paradigm, particularly in the “Warm Little Inflaton” scenario, up to date the simplest realization of warm inflation formulated within a concrete quantum field theory framework. We show that the symmetries of the model, required to avoid large thermal corrections to the inflationary potential, guarantee the stability of the inflaton at late times, while allowing for a smooth transition from an inflationary period to a radiation-dominated era. To conclude, we present our preliminary results for the inflaton dynamics during and after inflation and the associated constraints on the present inflaton mass, as well as prospects for future work.
Carlos García-Garcia: Dark energy from alpha-attractors: phenomenology and observational constraints
The possibility of linking inflation and late cosmic accelerated expansion using the $\alpha$-attractor models has received increasing attention due to their physical motivation. In the early universe, $\alpha$-attractors provide an inflationary mechanism compatible with Planck satellite CMB observations and predictive for future gravitational wave CMB modes. Additionally $\alpha$-attractors can be written as quintessence models with a potential that connects a power law regime with a plateau or uplifted exponential, allowing a late cosmic accelerated expansion that can mimic behavior near a cosmological constant. In this talk we study a generalized dark energy $\alpha$-attractor model. We thoroughly investigate its phenomenology, including the role of all model parameters and the possibility of large-scale tachyonic instability clustering. We verify the relation that $1+w\sim 1/\alpha$ (while the gravitational wave power $r\sim\alpha$) so these models predict that a signature should appear in either the primordial B-modes or in late time deviation from a cosmological constant. We constrain the model parameters with current datasets, including the cosmic microwave background (Planck 2015 compressed likelihood), baryon acoustic oscillations (BOSS DR12) and supernovae (Pantheon compressed). Our results show that expansion histories close to a cosmological constant exist in large regions of the parameter space, not requiring a fine-tuning of the parameters or initial conditions.
Francisco Pedro: Primordial black holes from single field inflation
I will discuss the formation of primordial black holes in the framework of single field inflation and present a string inflationary model allowing for their formation in the low mass region, where PBHs can account for a significant fraction of the dark matter abundance. The potential arises within type IIB flux compactifications and features a plateau at CMB scales and a near inflection point at large distance scales where the power spectrum is enhanced, thereby producing PBHs.
Miguel Zumalacárregui: No LIGO MACHO
Black hole mergers detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) have revived dark matter models based on primordial black holes (PBH) or other massive compact halo objects (MACHO). These objects would be abundant in the mass range 1-100 M_Sun, where rather remarkably, previous bounds were the weakest. I will present new constraints on the PBH abundance and mass using the gravitational lensing magnification of type Ia supernovae (Sne) using current datasets (JLA, Union 2.1). Our results rule out the hypothesis of MACHO/PBH comprising the totality of the dark matter at high significance in the mass range M > 0.01 M_Sun. Eliminating the possibility of a LIGO-mass MACHO further strengthens the case for microscopic dark matter.
José M. Sánchez-Velázquez: Dark Matter gravitational production in Reheating
In this talk I analyze the possibility that Dark Matter has been gravitationally produced during Reheating. I consider a scalar field non-minimally coupled to gravity as the responsible for DM. The behavior of the Ricci scalar of curvature will have an important impact on the behavior of the mode functions, enhancing the production of particles. Comparing the measures for DM abundance today we can put bounds on the parameters of the model.
Catarina Cosme: Scalar field dark matter with spontaneous symmetry breaking and the 3.5 keV line
We show that the present dark matter abundance can be accounted for by an oscillating scalar field that acquires both mass and a non-zero expectation value from interactions with the Higgs field. The dark matter scalar field can be sufficiently heavy during inflation, due to a non-minimal coupling to gravity, so as to avoid the generation of large isocurvature modes in the CMB anisotropies spectrum. The field begins oscillating after reheating, behaving as radiation until the electroweak phase transition and afterwards as non-relativistic matter. The scalar field becomes unstable, although sufficiently long-lived to account for dark matter, due to mass mixing with the Higgs boson, decaying mainly into photon pairs for masses below the MeV scale. In particular, for a mass of ∼7 keV, which is effectively the only free parameter, the model predicts a dark matter lifetime compatible with the recent galactic and extragalactic observations of a 3.5 keV X-ray line.
Clara Alvarez-Luna: Topological Dark Matter and PeV neutrinos
In this work, we explore the possibility of topological defects as viable dark matter candidates. The non-thermal production of magnetic monopoles by a phase transition is studied. The Kibble mechanism is analyzed, concluding that it is not a good approach to estimate their abundance and studying the corrections of the Kibble-Zurek model. We also study the effect of monopoles annihilation within this framework. The result of this analysis is that monopoles with a mass around the PeV provide a density compatible with PLANCK observations of the present dark matter density. In addition, recent observations of high energy neutrinos by IceCube show an spectrum that is not compatible with a power law that would be expected in a standard astrophysical scenario. We study the possibility that a decaying dark monopole with a mass in the PeV range provides a promising interpretation of the observed spectrum.
Javier Rubio: Primordial black holes from fifth forces
Primordial black holes can be produced by a long range attractive fifth force stronger than gravity, mediated by a light scalar field interacting with non-relativistic “heavy” particles. As soon as the energy fraction of heavy particles reaches a threshold, the fluctuations rapidly grow non-linear. The overdensities collapse into black holes or similar screened objects, without the need of any particular feature in the spectrum of primordial density fluctuations generated during inflation. I will discuss if such primordial black holes can constitute the total dark matter component in the Universe.
Tiago Barreiro: Removing the σ8 tension with coupled quintessence
A well-known problem of the ΛCDM model is the tension between the relatively high level of clustering, as quantified by the parameter σ8, found in cosmic microwave background experiments and the smaller one obtained from large-scale observations in the late Universe. In this paper we show that a coupled quintessence model can solve this problem if the background is taken to be identical to the ΛCDM one.
Angeles Moliné: Characterization of dark matter subhalo structural properties
Dark matter subhalos represent important probes of the mass accretion history and dynamics of host halos and thus, ultimately, of the underlaying cosmological model. The concentration of field halos has been extensively studied in the past and several concentration-mass relations have been proposed in the literature. In contrast, the study of subhalo properties represents a computational challenge due to the very large dynamic range which is required. In this talk a parametrization of the median subhalo concentration as a function of mass and distance from the host halo center will be presented.
Gonzalo J. Olmo: Modified gravity without modified gravity
In the past years we have shown that the charge without charge and mass without mass phenomenon introduced by Wheeler and Misner in the XXth century is rather common in certain metric-affine modified theories of gravity. I will discuss recent results regarding the possibility of describing modified gravity without modified gravity in the same family of theories.
Victor Afonso: Scalar Geons in Born-Infeld Gravity
The notion of ‘geon’, introduced by Wheeler to identify self-gravitating free electromagnetic fields, reappears in the metric-affine theories context in a natural way. In this talk we will briefly discuss the case of Born-Infeld Gravity model coupled to free scalar matter, in the metric-affine approach. Combining numerical methods and analytic approximations, we show that static, spherically symmetric, self-gravitating scalar field solutions indeed exist . Furthermore, we find that, depending on the ratio between the Schwarzschild radius and a length scale associated to the Born-Infeld theory, wormhole structures are spontaneously formed in the interior regions.
Joao Rosa: Black hole Lasers powered by Axion Superradiant instabilities
I will discuss how the superradiant instability of rotating black holes can produce dense axion clouds in their vicinity, and how stimulated axion decay into photon pairs can then lead to extremely powerful lasers. I will show, in particular, that the lasing threshold can be attained for axions with mass above 10^-8 eV forming superradiant clouds around spinning primordial black holes of sub-solar masses. Lasing is quenched by Schwinger pair production and the consequent formation of a critical electron-positron plasma, generating lasing bursts that can repeat once the plasma density becomes sub-critical after electron-positron annihilation. Interestingly, for 10^-5 eV axions, which may account for the majority of dark matter in the Universe, this leads to millisecond bursts in the GHz radio-frequency range, with peak luminosities around 10^42 erg/s, suggesting a possible link to the observed fast radio bursts.
David Mulryne: Numerical tools for multifield inflation
I will review the rich phenomenology of inflationary models with multiple scalar fields and discuss numerical tools that can be used to extract the observational signatures of such models, focusing on the PyTransport package.
Pedro Carrilho: General initial conditions for second order Boltzmann solvers
We study the initial evolution of general cosmological fluctuations at second order, after neutrino decoupling. We discuss the number of growing degrees of freedom and conclude that the neutrino velocity isocurvature unavoidably generates non-regular (decaying) modes at second order, thus effectively reducing the number of growing modes to 4 from the usual 5 present at linear order. We present approximate initial solutions for the transfer functions of all the relevant cosmological variables sourced by adiabatic and isocurvature modes at first and second order. We highlight the importance of mixed modes, which are sourced by two different isocurvature or adiabatic modes and do not exist at the linear level. In particular, we investigate the so-called compensated isocurvature mode and find non-trivial initial evolution when it is mixed with the adiabatic mode, in contrast to the result at linear order. Our results are then applied to the second order Boltzmann solver SONG to calculate the magnetic field generated by non-linear isocurvature modes in the pre-recombination epoch.
Jesús Torrado Cacho: Parameter estimation in Cosmology: new methods and new tools
I will discuss our work on building a machine-learning sampler that makes parameter estimation possible for models/likelihoods so slow that traditional MCMC sampling is overwhelmingly expensive. I will also present the new Python incarnation of CosmoMC: flexible, modular and aimed at rapid integration and testing of modified cosmological codes and fancy priors/likelihoods, without needing to touch CosmoMC’s source code.
Mar Bastero-Gil: Adiabatic out-of-equilibrium solutions to the Boltzmann equation
We show that a period of nearly constant Hubble rate and temperature lead to an adiabatic evolution of the number density of particles interacting with the thermal bath, even if thermal equilibrium cannot be maintained. In this case, the number density is suppressed compared to the equilibrium value but the associated phase-space distribution retains approximately an equilibrium form, with a smaller amplitude and a slightly smaller effective temperature. As an application, we explicitly construct a baryogenesis mechanism
during warm inflation based on the out-of-equilibrium decay of particles in such an adiabatically evolving state. We show that this generically leads to small baryon isocurvature perturbations, within the bounds set by the Planck satellite.
Prado Martín-Moruno: Avoiding the Big Rip in f(R) quantum cosmology
As is well known, extended theories of gravity provide us with an alternative to the dark energy paradigm. Being able to describe the same background cosmology, they can also predict the occurrence of a Big Rip singularity. In this talk, I will review how the Big Rip can be analysed in the framework of f(R) quantum geometrodynamics.
Mariam Bouhmadi-López: Classical and quantum approach to the little sibling of the big rip
We will start introducing what it is known as the little sibling of the big rip (LSBR). We will then show how this abrupt event can arise on the context of a minimally scalar field or a 3-form field. For these models, we will then carry a canonical quantisation \`a la Wheeler-DeWitt and apply the DeWitt condition to the wave function of the universe. It turns out that this condition is better fullfilled in the case of a minimally coupled scalar than a 3-form field.
Miguel Aparicio Resco: Model independent parametrization of growth in modified gravity
We propose fitting formulae for the growth function of matter density perturbations in modified gravity theories. We consider the model-independent approach based on the effective Newton constant, \mu(a,k)= G_{eff}/G, and find that f(a)=\beta(a) \Omega_{m}^{\gamma} (a) provides fits with accuracy below 1 %. We distinguish between three diffetent types of models: \mu=\mu(k), \mu=\mu(a) and \mu=\mu(a,k). In each case, we present the procedure to find analytical fitting formulas and consider some examples. Finally, we show how the obtained functions can be applied in Fisher matrix forecast analysis.
Gabriel Farrugia: Cosmological reconstructed solutions in extended teleparallel gravity theories with a teleparallel Gauss-Bonnet term
In this talk, the theory of f(T; TG) gravity is presented in 3+1 dimensions where T is the torsion scalar and TG is the teleparallel analogue of the Gauss-Bonnet term. We focus on the standard Friedmann-Lemaitre-Robertson-Walker geometry to reconstruct gravitational Lagrangians capable of mimicking various types of cosmological solutions, from power-law solutions to bouncing cosmologies. In particular, the aim is to reconstruct Lagrangians in which the cosmological constant is not required; instead, a perfect fluid shall be considered. We find that Lagrangians without a cosmological constant can be constructed for LCDM cosmology and hence may compete with other extensions of General Relativity.
Lara Sousa: On the matter Lagrangian of particles and fluids
We consider a model where particles are described as localized concentrations of energy, with fixed rest mass and structure, which are not significantly affected by their self-induced gravitational field. We show that the volume average of the on-shell matter Lagrangian Lm describing such particles, in the proper frame, is equal to the volume average of the trace T of the energy-momentum tensor in the same frame, independently of the particle’s structure and constitution. Since both Lm and T are scalars, and thus independent of the reference frame, this result is also applicable to collections of moving particles and, in particular, to those which can be described by a perfect fluid. Our results are expected to be particularly relevant in the case of modified theories of gravity with non-minimal coupling to matter where the matter Lagrangian appears explicitly in the equations of motion of the gravitational and matter fields, such as f(R,Lm) and f(R,T) gravity. In particular, they indicate that, in this context, f(R,Lm) theories may be regarded as a subclass of f(R,T) gravity.
Rui Azevedo: Perfect fluid Lagrangian and its cosmological implications in non-minimally coupled theories of gravity.
In non-minimally coupled theories of gravity, the Lagrangian density of matter appears explicitly in the equations of motion for the metric fields. Therefore, it is essential to ascertain the form that such a Lagrangian should take. In this presentation we will go over a recent proposal that if a perfect fluid is constituted by localized concentrations of energy with fixed rest mass and structure (solitons) then the average on-shell Lagrangian of a perfect fluids is given by L=T, where T is the trace of the energy-momentum tensor. This result is shown to have profound implications for the aforementioned theories, potentially leading to observable deviations from a black-body cosmological background radiation spectrum and to changes in the predicted baryon-to-photon ratio.
Marina Cortés: Irreversibility in Foundational Cosmology
I present arguments for considering time irreversibility in Early Universe cosmology and the current theoretical problems it addresses, including the initial conditions measure problem. I introduce the proposal I’ve developed that the arrow of time of the universe is present in the microscopic level and not only in the macroscopic regime of thermodynamics.
Cláudio Gomes: Gravitational waves in theories with a non-minimal curvature-matter coupling
Gravitational waves from theories with a non-minimal coupling between matter and curvature are analysed with a cosmological constant and dark energy-like fluids both in the perturbation theory and Newman-Penrose formalisms.
Ricardo Zambujal Ferreira: Thai-flation
The phenomenology of an axial coupling during inflation between axions and gauge fields has been a topic of great interest. The coupling can trigger an instability in the gauge fields leading to strong particle production. This can give rise to large corrections to the spectrum of perturbations and/or even to backreaction on the background. I will show that there is a regime which has been missing in the literature. Because scatterings and decays depend strongly on the particle number, if the particle number reaches a given value the system can thermalize and dramatically change the predictions of this scenario.
Bruno Barros: Traversable wormholes with 3-forms
Wormholes are tunnels connecting two different regions of spacetime and have been a subject of discussion for almost 100 years. In this talk it will be shown that it is possible to equip a static and spherically symmetric wormhole with a 3-form field, solve the Einstein field equations and find solutions in which the form field holds the wormhole open, behaving as a phantom energy source.
Francisco Cabral: Phase transition with U(1) symmetry breaking in Einstein-Cartan-Theory
Phase transitions motivate the study of processes in which the U(1) Symmetry of electromagnetism is explicitly broken. In the Einstein-Cartan-Sciama-Kibble theory of gravity, the spacetime torsion might be relevant for understanding the physics of phase transitions at very high densities (and very small scales), providing the framework for a gravity induced mechanism of the U(1) symmetry breaking. After a brief overview on gauge theories of gravity and its relation to non-Riemann geometries, In this talk, we will analyse the (generalized) Einstein-Cartan-Dirac-Maxwell theory allowing the direct coupling between the electromagnetic 4-potential and torsion. This coupling gives an explicit U(1) symmetry breaking and new physics relevant for the cosmology of the very early Universe. We get generalized gravitational, electromagnetic and Dirac equations. Possible applications of the theory and some parallels to Proca fields and superconductivity will be briefly considered.
Joao Luis Rosa: Cosmological solutions in generalized hybrid metric-Palatini gravity
We construct exact solutions representing a Friedmann-Lemaitre-Robsertson-Walker (FLRW) universe in a generalized hybrid metric-Palatini theory. By writing the gravitational action in a scalartensor representation, the new solutions are obtained by either making an ansatz on the scale factor or on the effective potential. Among other relevant results, we show that it is possible to obtain exponentially expanding solutions for flat universes even when the cosmology is not purely vacuum.
